Antioxidant Phenols in Barley (Hordeum vulgare L.) Flour:  Comparative Spectrophotometric Study among Extraction Methods of Free and Bound Phenolic Compounds

Abstract

Phenolic compounds are found in both free and bound forms in cereals. The majority is in the insoluble bound form, that is, bound to cell wall material, such as ferulic acid and its derivatives. The antioxidant properties of the phenolic compounds in grains are associated with the health benefits of grains and grain products. The extraction capacity of several solvent mixtures, for extracting free phenols from barley flours, and the possibility of employing a rapid automated solvent extraction method were studied. The extraction yield of each method was evaluated by correlating several spectrophotometric indices (absorption at 280, 320, and 370 nm and total phenolic compounds by the Folin-Ciocalteu method) with the antioxidant activities of the barley extracts (scavenging activity by the 2,2-diphenyl-1-picrylhydrazyl method). Interesting results were obtained when ethanol and acetone-based extraction mixtures were employed to extract free phenols. A comparison was made between alkaline and acid hydrolysis. The extraction yield of bound phenolic compounds increased when the digestion time for alkaline hydrolysis was prolonged.

Comparison of Antioxidant Activity of Barley (Hordeum vulgare L.) and Malt Extracts with the Content of Free Phenolic Compounds Measured by High Performance Liquid Chromatography Coupled with CoulArray Detector

“…We supposed that these compounds should be mainly responsible for the antioxidant properties of barley, as Zhao et al 29 reported. However the results indicate that in water extracts, high molecular phenolics were present and more responsible for the antioxidant activity of barley 3 . In the case of malt, a significant positive correlation was found between the content of ferulic acid and ITT (n = 10, r = 0.747, p < 0.05) and content of catechin (n = 10, r = 0.767, p < 0.05).…”

“…About 80% of beer polyphenols originate from malt and the remaining 20% come from hop 9,18 . The phenolic compounds in barley include phenolic acids (benzoic and cinnamic acid derivatives), flavonoids, proanthocyanidins, tannins, and amino phenolic compounds 3 .…”

Fenóis totais e atividade antioxidante de cinco plantas medicinais

“…A quantificação espectrométrica de compostos fenólicos é realizada por meio de uma variedade de técnicas, todavia, a que utiliza o reagente de Folin-Ciocalteu figura entre as mais extensivamente utilizadas 2,4,7,9,10 . O reagente consiste de mistura dos ácidos fosfomolibídico e fosfotunguístico, no qual o molibdênio e o tungstênio encontram-se no estado de oxidação 6 + porém, em presença de certos agentes redutores, como os compostos fenólicos, formam-se os chamados molibdênio azul e tungstênio azul, nos quais a média do estado de oxidação dos metais está entre 5 e 6 e cuja coloração permite a determinação da concentração das substâncias redutoras, que não necessariamente precisam ter natureza fenólica 4,11 .…”

“…A determinação do teor de fenóis totais presentes nas amostras de extrato etanólico das espécies estudadas foi feita por meio de espectroscopia na região do visível utilizando o método de Folin-Ciocalteu com modificações 7 . O extrato etanólico (100 mg) foi dissolvido em metanol, transferido quantitativamente para um balão volumétrico de 100 mL e o volume final foi completado com metanol.…”

Estudos químicos e biológicos de Microgramma vacciniifolia (Langsd. & Fisch.) Copel (Polypodiaceae)

“…7,8 Os extratos e frações (5 mg) foram dissolvidos em 5 mL de metanol. Uma alíquota de 100 µL desta solução foi transferida para balões de 5 mL.…”